Tomato is eaten worldwide and also abundantly contains vitamins, minerals, lycopene and the like so that it is highly nutritious.
However, in terms of the area suitable for the cultivation thereof, sufficient growth is not always expected in any place and it is difficult in some areas to provide fresh fruits thereof. For example, for the cultivation thereof in an area where ambient temperature is high, the wilting of the plant body due to the heat has been a big problem in the growth of tomato plants.
Examples of an approach in plant breeding to solve this problem include breeding a tomato having an excellent heat resistance phenotype. An increased vigor in the plant body, that is, a combination of an increased plant height and an increased stem diameter is included as one of the important phenotypes thereof.
The height of a plant body is known to be increased in tomato by replacing valine at position 302 with glutamic acid in the amino acid sequence of the Della protein having a function to prevent the growth of a plant (Non-Patent Document 1). However, because it has been reported that the height of a plant body is decreased or increased in rice by a mutation introduced in other regions of the Della protein, it is not sufficient for an increase in plant vigor to simply introduce a mutation in the DELLA gene (Non-Patent Documents 2 and 3).
Meanwhile, the thickness of a stem, which holds a plant itself, likewise plays an important role in the heat resistance in plants and the thickening of a stem is a useful phenotype against the wilting due to the heat. In tomato, various reports have been made on the relationship between gene mutations and the expression of phenotypes but any mutation related to the phenotypic expression of increased stem diameter has not been found.